Cleaning surface deposits from raschig rings



United States Patent Office 3,452,490 Patented July 1, 1969 Int. Cl.B24]: 1/00 US. Cl. 51-314 7 Claims ABSTRACT OF THE DISCLOSURE Surfacedeposits are cleaned from Raschig rings by tumbling same with anabrasive such as sand. The Raschig ring and sand mix can be tumbled dryor wetted with a cleaning solution. The method is especially suitablefor cleaning dirty or fouled Raschig rings constructed of aluminum. Thetumbling is advantageously carried out at elevated temperatures on theorder of about 100 to 200 F.

This invention relates to cleaning surface deposits from Raschig ringsused in processing equipment, and more particularly relates to animproved method of cleaning carbonaceous and/or polymeric deposits fromdirty or fouled Raschig rings used as packing in commercial distillationor extraction columns, so that they may be reused by tumbling theRaschig rings together with an abrasive such as sand.

Raschig rings are well-known packing materials used for a plethora ofvarying processes. In distillation towers and many other process vesselsor other equipment related to varying process steps, the conditionsprevailing in the vessel operate on the materials being processed tocause surface deposits of widely differing natures and as a result of avirtual plethora of phenomena to form on the inner and outer surfaces ofthe Raschig rings. When such deposits form, it becomes necessary fromtime to time either to remove these deposits or to replace the coatedRaschig rings with a fresh charge of clean Raschig rings. In cases wherethe rings are cleaned, those deposits which are diflicult to remove,which is the usual case, require severe methods to clean the rings,especially the inner annular surfaces thereof. The simplest, mosteffective, convenient, least time consuming methods of cleaning therings all over, including the inner surfaces, heretofore has been by oneor the other of two fairly competitive methods: (1) by treating therings with highly corrosive or caustic cleaning solutions or (2) byburning the deposits off. These techniques, however, frequently damagethe rings due to the severity of the treatment. The damage problem isgreatly accentuated when the rings are constructed of materials such asaluminum which is attacked by the highly caustic solutions and weakenedstructurally by the heats of the burning techniques.

It is, accordingly, highly desirous to find a technique of cleaningRaschig rings which minimizes damage to the ring surfaces and structuregenerally.

A special object is to provide a method suitable for cleaning Raschigrings constructed of materials such as aluminum.

Other objects are to provide a technique broadly applicable to Raschigrings constructed of different materials, which will reduce the costsand the time involved in removing surface deposits.

Still another object is to provide a broad method generally applicableto the removal of various and different kinds of surface deposits fromall surfaces of Raschig rings, including the inaccessible innersurfaces.

Other objects will become apparent from viewing this disclosure in itsentirety.

To the accomplishment of the foregoing and related ends, the presentinvention comprises in brief and broadest respect, admixing the Raschigrings with sand or other abrasive and subjecting the mix to tumblingaction. In more narrow but still broad respect the invention comprisesthe alteration of additional treatments of the mix of (1) applying heatsufiicient to obtain temperatures in the range of about F. to 200 F.whereby it is tumbled dry and free of lumps; or adding a cleaningsolution thereto such as an aqueous caustic solution and tumbling samein a very wet state.

We have found that the sand and Raschig ring mix should either be drywith regard to both Water and organic matter, or else very wet with acleaning solution.

Usually at least about 0.1 volume of sand per volume of Raschig ringsare used. On the other hand, not more than about 0.4 volume of sand pervolume of Raschig rings are employed because of reduced efliciency interms of the amount of rings cleaned per volume of tumbler, andultimately in the time required to clean large volumes of rings, etc.,although such would undoubtedly work. Preferably about 0.2 to 0.3 volumeof sand per volume of Raschig rings is employed.

One cautionary comment is in order in connection with the tumblingoperation. Although the present invention is applicable to clean Raschigrings of all materials of construction, the tumbling action is to beconducted with care in the case of ceramic and such materials unable totake considerable shock unlike those constructed of steel and aluminum.A padded tumbler can be used as a means to reduce the shock duringtumbling. 'Ihe tumbling action is conveniently and effectively achievedby using known and existing equipment such as a concrete mixer, althoughother equipment capable of a regulated tumbling already known can beused or easily devised.

The heat is conveniently applied in the dry technique, where thattechnique is used, by inserting a large blowtorch of the kerosene fueledtype into the opening of the mixer, although other heating means canalso be used. During the tumbling, temperatures of the sand and Raschigmix as high as about 200 F. may be desired, but typically the mix isheated to about 100 to 150 F., and preferably it is heated to about toF.

When a cleaning solution is used, it should be one that dissolves thedeposit or otherwise actively aids the loosening or removal of thisdeposit as by reaction therewith or operating thereon. It can be anaqueous solution of a wetting agent, a detergent, an alkaline material,or an acid depending on the particular deposit. It should not be toocorrosive on the tumbler or Raschig rings and preferably is completelycompatible with the mateirals of construction in the mixer or Raschigrings. Generally a suitable cleaning agent will already be known for theparticular deposit but if not a suitable one can be determined byroutine experimentation. Generally the concentration is selected tominimize corrosion of the equipment and the Raschig rings, if it iscorrosive at all on either, subject to the limitation that aconcentration ufiicient to be effective as a cleaning aid is always tobe employed. Examples of materials that may be used as cleaningsolutions alone and some in combination are sodium hydroxide, potassiumhydroxide, sulfuric acid, nitric acid, trichloroethylene, methanol,dimethyl sulfoxide, citric acid, sulfamic acid, sodium naphthenate,sodium sulfonates and sodium carbonate, etc. Certain of the foregoingare known to present some hazard in regard to toxicity and/orflammability, but this can be easily obviated by proper precautionsreadily apparent to those skilled in the art. The reason why cleaningsolutions can be used here is that the use of sand shortens the cleaningoperation sufficiently that the Raschig rings are not harmed bycorrosive cleaning solutions nearly so much as in conventionaltechniques using the same cleaning solutions. Batches of Raschig ringshave been cleaned in about ten minutes using sand wetted with cleaningsolution. The rings are not significantly damaged by the dilute causticcleaning solutions at such short contact times.

The amount of cleaning solution to be used is not critical but enough isused to completely wet the abrasive and Raschig ring mix. Typicallyabout 0.1 to 0.2 volumes of cleaning solution per volume of Raschigrings is used.

To facilitate the understanding of the invention, certain details andillustrative embodiments will now be set forth; however, of course, itis to be fully understood and appreciated that the invention is notlimited to the specific conditions or details set forth in theseexamples, since the process is capable of many modifications andvariations and conditions, such modifications and variations beingaided, suggested, or indicated by the discussion of the EXAMPLE 1 Drycleaning About 30 ft. of Raschig rings were placed in a charge hopper.400 pounds of No. 2 sandblasting sand were added and the mix charged toa conventional /2 yard concrete mixer and tumbled for 20-30 minutes.During the tumbling a large kerosene fueled blow-torch (about 3" nozzle)was placed in the charge opening to provide heat for drying. Aftertumbling for a time within the foregoing range but sufficient to removemost of the deposit, the mixer contents were dumped onto about a A" to/2" mesh wire screen and water washed with a hose to remove loose sandand deposit.

EXAMPLE 2 Wet cleaning About 30 ft. of Raschig rings were placed in acharge hopper. 100 pounds of No. 2 sandblasting sand, 30 gallons of hotwater (about 180 F.) and 1 pound of Oakite 77 (a designation of OakiteProducts Inc. for an alkaline cleaning material it markets) were added.The mix was then charged to a concrete mixer (described above) and ,wastumbledfor about minutes..The contents of the mixer was then dumped ontoa coarse screen and water washed similar to Example 1 to remove theloose sand and deposit and residual cleaning chemical.

We claim:

1. A method of cleaning deposits from fouled Raschig rings constructedof aluminum wherein said deposits have been formed on said Raschig ringsby their use as'a packing in a distillation or solvent extraction columnwhich comprises admixing said fouled Raschig rings with sand to form amixture and subjecting said mixture to a tumbling action.

2. A method according to claim 1 wherein said mixture is tumbled at atemperature in the range of about lOO to 200 F. 3. A method according toclaim 1 wherein about 0.1

to 0.4 volumes of sand per volume of Raschig rings is used.

. 4. A method according to claim 1 wherein a cleaning solution is addedto said sand and Raschig ring mixture and the so formed wet mixture istumbled in the wet state.

5. A method according to cleaim 4 wherein said mixture is tumbled at atemperature in the range of about to 200 F. r

6. A method according to claim 5 wherein the cleaning solution comprisesa mixture of sodium hydroxide and sodium carbonate.

- 7. A method according to claim 6 wherein about 0.1 to 0.4 volumes ofsand per volume of Raschig rings and about 0.1 to 0.2 volume of saidcleaning solution per volume of rings is employed.

References Cited UNITED STATES PATENTS 'LESTER M. SWINGLE, PrimarExaminer.

US. Cl. X.R. 134-7, 25, 33

